1. Field of the Invention
This invention relates to a metal deposited film forming method, particularly to a process for forming metal deposited film which can be preferably applied to wiring of semiconductor integrated circuit device, etc.
2. Related Background Art
For electrode or wiring in electronic device or integrated circuit by use of semiconductor of the prior art, aluminum (Al) or aluminum containing silicon (Al--Si), etc. has been primarily used. Here, Al is inexpensive, has high electroconductivity, and also a dense oxide film is formed on the surface, whereby it has many advantages such that it can be chemically protected internally to be stabilized, that adhesiveness with Si is good, etc.
Whereas, integration degree of integrated circuit such as LSI, etc. is increased, and fine formation of wiring and multi-layer wiring are particularly required in recent years. Thus, more stringent demands not found to date are presented for wiring. For example, in dynamic RAM such as 4 Mbit or 16 Mbit, etc., the aspect ratio (depth of opening diameter of opening) of openings (via-holes) in which a metal such as Al, etc. must be deposited is 1.0 or more. The diameter itself of the opening is 1 .mu.m or less, and a technique capable of depositing Al as well in openings with larger aspect ratio is required.
Besides, to be commercially successful concerning semiconductor integrated circuit devices, the technique must enable bulk production at low cost.
There have been known in the art the sputtering method, the gas phase method such as the CVD method by use of trimethylaluminum, etc. as a method of forming metal film such as Al film, etc. Above all, the thermal CVD (chemical vapor deposition) method has been variously studied. For example, there has been employed the method in which an organic aluminum dispersed in a carrier gas is transported onto a heated substrate, and the gas molecules are thermally decomposed on the substrate to form a film. For example, as described in "Journal of Electrochemical Society Vol. 131, p. 2175 (1984)", by use of triisobutyl aluminum (i-C.sub.4 H.sub.9).sub.3 Al (TIBA), film formation is carried out at a film formation temperature of 260.degree. C., a reaction tube pressure of 0.5 Torr, whereby a film of 3.4.mu. cm is formed.
However, according to this method, the surface flatness of Al is poor, and no film of good quality is obtained in view of step coverage, electromigration, etc. Besides, the Al within openings do not become dense.
Japanese Patent Laid-open No. 63-33569 discloses a method for film formation by heating an organic aluminum in the vicinity of the substrate. According to this method, Al can be deposited according to the CVD method selectively only on the metal or semiconductor surface of the substrate where the naturally oxidized film on the surface has been removed. It is further possible to deposit Al on the oxide film by the sputtering method after embedding of the openings.
However, according to this method, since the surface smoothness of Al within an opening is a major premise it is not sufficient, as electrical contact of the interface between the Al film according to the CVD method and the Al film according to the sputtering method is poor in bringing about an increase in resistivity.
As an example of a modification of this method, the pre-text of "2nd Symposium of Electrochemical Society, Branch of Japan (Jul. 7th, 1989), on p. 75, described the double wall CVD method. This method can grow selectively Al only on a metal or semiconductor by use of TIBA gas. However, it is difficult to precisely control the difference between the gas temperature and the substrate surface temperature and the bomb and the wiring must also be heated. As these factors add to the drawback that the apparatus constitution becomes complicated.
More specifically, if these are to be controlled, the apparatus for metal deposited film formation is complicated and it cannot be made as the sheet treatment type in which deposition can be effected in only one sheet of wafer by one deposition process. Besides, only a film which can never be said to be of good quality can be obtained at a deposition speed of 500 .ANG./min. at the highest, whereby it is impossible to realize the output necessary for bulk production. Moreover, even the film obtained according to this method cannot become a uniform continuous film unless made to have some thickness. Thus, this method proved to be unsatisfactory and unsuitable for bulk production, because reproducibility was poor for such reasons that flatness of the film is poor, that selectivity of Al selective growth cannot be maintained for so long time, etc.
Further, when one metal film forming apparatus is employed, various gases for film formation or gases for cleaning of the chamber, etc. are introduced into a reaction chamber for the purpose of film formation actuation or maintenance of the apparatus to carry out the desired treatments. When film formation is continued while performing such treatments, even in the CVD method with little containment of carbon, etc. from an organic aluminum starting material, there will ensue the fear that various impurities other than carbon may be entrained into the interface, etc. Such a problem may suddenly cause a to lower yield in bulk production of semiconductor devices.